Developing millimeter-scale indentation to probe local cellular environments

Abstract

It was found that agarose indentation elastic modulus increases with concentration (w/v) and that stress-relaxation properties generally remain constant across concentrations. Solvent-type and aging of agarose over a two week period do not change indentation elastic modulus. In addition, this indentation technique is capable of measuring the mechanical properties of other in vitro models and tissue materials. Fiber-reinforced hydrogels, a novel hybrid fiber-gel in vitro ECM model, were tested as an additional in vitro material. Explant tissue, rat mammary glands, were also measured for comparison with in vitro models. Overall, this milli-scale indentation provides a versatile technique to assess elastic and viscoelastic material properties for improved design and development of in vitro models for a wide range of tissue engineering applications.

Mechanical characteristics of cellular environments such as the extracellular matrix (ECM) play an important role in influencing cellular behavior and fate. When these mechanical properties are disrupted as in disease, there is a dysregulation in cellular behavior that can lead to worsening prognosis. For this reason, the development of mechanically accurate ECM-mimicking in vitro models is of the utmost importance. Mechanical characterization of these models is performed on a variety of length-scales pertinent to the level of investigation of a given study. We are interested in probing the mechanisms of mechanosensing and force transduction at the single cell to tumor spheroid length scale, microns to millimeters. Current mechanical characterization techniques are able to probe at the cellular mechanosensing level, but do not recapitulate the rates at which cells themselves load their environments. Thus, we have developed a millimeter-scale indentation technique capable of loading materials at more physiologically relevant loading rates. We have extensively measured agarose hydrogel as a validation material for the development of this indentation method.